Modern computer systems often comprise a plurality of operating devices and a shared resource. The operating devices can comprise, e.g., I/O controllers such as serial communication controllers in a line interface card arranged to couple a plurality of data transmission lines through corresponding modems to a processor. The processor is therefore shared by the communication controllers to process data, typically in the form of data packets, received at or to be transmitted by the serial communication controllers.
In known computer systems, a common memory is used to buffer data packets between the shared processor and the serial communication controllers. The common memory is typically divided into a plurality of buffers and each serial communication controller is allocated a fixed number of buffers for buffering of data packets received at or to be transmitted by the respective serial communication controller. Each data packet is stored in a separate buffer, but a single data packet may be stored in several buffers if its size is larger than the buffer size. The shared processor polls the buffers in a round robin fashion, through a sequence of time slots, to process one buffer per time slot.
However, in many applications, the data packets received at or transmitted by each of the serial communication controllers may vary in size from a few bytes to several bytes in length. The amount of processing time required to process each data packet is approximately proportional to the size of the data packet. A serial communication controller that typically receives relatively large data packets can dominate the use of the shared processor when the processor follows a round robin schedule that fixes the processing of data packets to one buffer per time slot. This is because each relatively large data packet may completely fill one buffer and may even fill more than one buffer. Thus, the shared processor will be required to process a relatively large amount of data during each time slot allocated to the buffers of the serial communication controller receiving relatively large data packets.
A serial communication controller that receives a series of relatively small data packets will, on the other hand, only partially fill each one of several buffers, one data packet per buffer, with only one of its buffers being processed by the shared processor during each round robin polling cycle. The serial communication controller may therefore run out of available buffers before the shared processor can completely process all of the relatively small data packets. Thus, the one buffer per time slot processing scheme typically utilized in computer systems is often deficient in operating environments wherein the amount of data requests to be processed during each scheduled time slot varies greatly from device to device.